xfs: Ensure inode allocation buffers are fully replayed

With delayed logging, we can get inode allocation buffers in the
same transaction inode unlink buffers. We don't currently mark inode
allocation buffers in the log, so inode unlink buffers take
precedence over allocation buffers.

The result is that when they are combined into the same checkpoint,
only the unlinked inode chain fields are replayed, resulting in
uninitialised inode buffers being detected when the next inode
modification is replayed.

To fix this, we need to ensure that we do not set the inode buffer
flag in the buffer log item format flags if the inode allocation has
not already hit the log. To avoid requiring a change to log
recovery, we really need to make this a modification that relies
only on in-memory sate.

We can do this by checking during buffer log formatting (while the
CIL cannot be flushed) if we are still in the same sequence when we
commit the unlink transaction as the inode allocation transaction.
If we are, then we do not add the inode buffer flag to the buffer
log format item flags. This means the entire buffer will be
replayed, not just the unlinked fields. We do this while
CIL flusheѕ are locked out to ensure that we don't race with the
sequence numbers changing and hence fail to put the inode buffer
flag in the buffer format flags when we really need to.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 9b21f80f31ce..bb17cc044bf3 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -200,6 +200,15 @@ xlog_cil_insert(
         ctx->nvecs += diff_iovecs;
 
         /*
+         * If this is the first time the item is being committed to the CIL,
+         * store the sequence number on the log item so we can tell
+         * in future commits whether this is the first checkpoint the item is
+         * being committed into.
+         */
+        if (!item->li_seq)
+                item->li_seq = ctx->sequence;
+
+        /*
          * Now transfer enough transaction reservation to the context ticket
          * for the checkpoint. The context ticket is special - the unit
          * reservation has to grow as well as the current reservation as we
@@ -325,6 +334,10 @@ xlog_cil_free_logvec(
  * For more specific information about the order of operations in
  * xfs_log_commit_cil() please refer to the comments in
  * xfs_trans_commit_iclog().
+ *
+ * Called with the context lock already held in read mode to lock out
+ * background commit, returns without it held once background commits are
+ * allowed again.
  */
 int
 xfs_log_commit_cil(
@@ -678,3 +691,35 @@ restart:
         spin_unlock(&cil->xc_cil_lock);
         return commit_lsn;
 }
+
+/*
+ * Check if the current log item was first committed in this sequence.
+ * We can't rely on just the log item being in the CIL, we have to check
+ * the recorded commit sequence number.
+ *
+ * Note: for this to be used in a non-racy manner, it has to be called with
+ * CIL flushing locked out. As a result, it should only be used during the
+ * transaction commit process when deciding what to format into the item.
+ */
+bool
+xfs_log_item_in_current_chkpt(
+        struct xfs_log_item *lip)
+{
+        struct xfs_cil_ctx *ctx;
+
+        if (!(lip->li_mountp->m_flags & XFS_MOUNT_DELAYLOG))
+                return false;
+        if (list_empty(&lip->li_cil))
+                return false;
+
+        ctx = lip->li_mountp->m_log->l_cilp->xc_ctx;
+
+        /*
+         * li_seq is written on the first commit of a log item to record the
+         * first checkpoint it is written to. Hence if it is different to the
+         * current sequence, we're in a new checkpoint.
+         */
+        if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
+                return false;
+        return true;
+}